1. Field of the Invention
This invention relates to methods and compositions exhibiting synergistic antimicrobial (biocidal) activity using a combination of 1-(3-chloroallyl)-3,5,7 triaza-1-azoniaadamantane chloride and 2-bromo-2-nitropropane-1,3-diol. The methods and compositions of the invention are very effective in preventing microbial spoilage of aqueous mineral and ore slurries and in paper and pulp preparation.
2. Description of the Prior Art
Various ores contain minerals that must be separated and purified to achieve their final useful state. A representative example of this type of separation process is the mining and separating of kaolin clay from the tailings. In the U.S., kaolin is mined from the middle Georgia clay belt with a dragline operation. An overburden of red soil is removed to reach the kaolin which can vary from a cream color to gray. Crude clay from various properties is sent to a crude clay storage.
The first step in the processing is called blunging. Crude clay having different properties can be blended at this point to give desired characteristics in the final product. Blunging is a high shear process used to slurry the ore at 50% to 60% solids in water. Inorganic dispersants such as hexametaphosphate, tripolyphosphate, and silicate are normally added to reduce the viscosity of the slurry. pH is adjusted to the basic side with sodium carbonate.
After the pH is adjusted, the slurry is degritted with a dragbox to remove large particles. Degritted slurry having different properties is sometime blended at this point. The crude slurry is then sent to centrifuges to reduce the size of 90% to 92% of the slurry to less than 2 .mu.m for a fine clay. A coarse clay may be on the order of 90% of the slurry reduced to less than 75 .mu.m.
High gradient magnetic separators are used to remove TiO.sub.2 and iron oxide impurities from the crude slurry. Magnetic strength is 1.5 to 2.0 tesla. If desired, the clay is then delaminated in attrition mills. If a clay has a high organic content, it is treated with ozone at this point for color reduction. Next, the clay is leached with sodium bisulfite at pH.congruent.3. Ferric iron is reduced to ferrous and brought into solution. The leached slurry is then filtered and ferrous iron removed in the filtrate. In the next step, a portion of the filter cake is redispersed in water using organic dispersants. Biocides may be added in both the filtration and dispersing steps.
A second portion of the filter cake is spray dried and the final product is made by combining the blunged filter cake with spray dried material to give about a 70% solids product. Additional dispersant and biocide is often added at this time.
Known biocidal compositions have been either unsuccessful or uneconomical in removing microbiological contamination from these ore and mineral processing slurries. Accordingly, a biocide capable of economically removing microbiological contaminants without adversely affecting the final clay product is desired.